The present invention relates generally to compound differential planetary gear assemblies, and, more particularly, to improved compound differential planetary gear assemblies in which first and second ring gears are arranged alternately in an axial stack, and wherein each planet gear has a constant gear-tooth cross-section along the length of this stack in meshing engagement with each of the first and second ring gears such that loads transmitted between the ring and planet gears will act in alternate directions along the length of the stack.
Compound differential planetary or epicyclic gear trains are known. Basically, these devices include a central sun gear, a plurality of planet gears arranged to rotate about the sun gear, and at least two outer ring gears in meshing engagement with the planet gears. Such planetary gearing may be used, for example, to transmit relatively high torques between the ring gears.
Compound differential planetary gear assemblies have been used as an actuating hinge. One application has been to control an aircraft flap surface with respect to a wing structure. In practice, such a prior art arrangement has an input shaft operatively arranged to drive a sun gear, a plurality of planet gears arranged to rotate about the sun gear, and first and second ring gears in meshing engagement with the planet gears. The first and second ring gears have different numbers of teeth such that, as the sun gear is rotated, the differential number of teeth causes one ring gear to move relative to the other ring gear. In this prior art arrangement, the planet gears are formed with gear teeth portions having different pitch diameters, depending upon the particular ring gear they are adapted to engage. This type of planet gear is expensive to manufacture because of the different gear teeth that must be hobbed thereon at different portions of its axial extent. Moreover, this arrangement, with relatively large axial separation between the alternating loads on the planet gear shaft, causes bending of the shaft and necessitates crowning of the gear teeth in order to attain high torques.
U.S. Pat. No. 4,942,781, the aggregate disclosure of which is hereby incorporated by reference, discloses a form of differential planetary gear assembly having a sun gear, a plurality of planet gears, and a plurality of ring gears. The ring gears have different numbers of teeth. As shown in FIG. 3 of this patent, the planet gears have a constant gear-tooth cross-section along the portion that is engaged with the two ring gears. This is possible by modifying the tooth pitch of the ring gears to mesh with a constant tooth pitch on the planetary gears. This techniques is utilized in the following described invention.
Accordingly, it would be desirable to provide an improved compound differential planetary gear assembly that permits the use of planet gears that have a constant gear-tooth cross-section along the portion thereof that is in meshing engagement with the ring gears, and that distributes the load along the length of the alternating ring gear segments.
With parenthetical reference to the corresponding parts, portions or surfaces of the disclosed embodiment, merely for purposes of illustration and not by way of limitation, the present invention broadly provides an improved compound differential planetary gear assembly (50).
The improved gear assembly broadly includes a sun gear (52), a plurality of planet gears (53) engaging the sun gear, a plurality of first ring gears (54), and a plurality of second ring gears (55). Each of the second ring gears has a number of teeth different from that of the first ring gears. The first and second ring gears are arranged alternately in an axial stack. Each planet gear has a constant gear-tooth cross-section (62) along the length of the stack in meshing engagement with each of the first and second ring gears. Loads transmitted between the first and second ring gears and the planets will therefore be distributed and act in alternate directions along the length of the stack.
The assembly may further comprise a plurality of separator rings (60) operatively arranged between the planet gears at each end of the stack. Each ring gear may have an annular bearing tongue (65) that extends toward an adjacent ring gear in a stack, with the adjacent ring gear having an annular bearing groove (66) to receive such tongue. The housing may have an annular bearing tongue, and the ring gear positioned adjacent the housing may have an annular bearing groove adapted to be receive such housing tongue. The housing may also have an annular bearing groove, such that the ring gear positioned adjacent that housing will have an annular bearing tongue that is adapted to extend into such housing groove. The plurality of the first ring gears may be different from the plurality of the second ring gears.
Accordingly, the general object of this invention is to provide an improved compound differential planetary gear assembly.
Another object is to provide an improved compound differential planetary gear assembly having a plurality of first and second ring gear sections arranged alternately in an axial stack so as to distribute the load along the stack and along the meshing elongated planet gears so as to prevent bending of the planet gears, and the concomitant need for crowning of the gear teeth.
Still another object is to provide an improved compound differential planetary gear assembly in which each planet gear has a constant gear-tooth cross-section along the length of such stack in meshing engagement with each of the first and second ring gears.
These and other objects and advantages will become apparent from the foregoing and ongoing written specification, the drawings, and the appended claims.